Dithiophosphates as lubricant antioxidents and anti-corrosion agents

ABSTRACT

Compounds of the formula ##STR1## wherein the symbols R 1  to R 9  have the meanings given in claim 1, are suitable as extreme pressure and antiwear additives in lubricants. The compounds contain as radicals R 5  or R 7  a group of the formula ##STR2## wherein R 10  and R 11  have the meanings given in claim 1. The compounds according to the invention are characterized also as good antioxidants and anti-corrosion agents.

The present invention relates to dithiophosphates, to their use aslubricant additives, to the production of the novel compounds, and tothe lubricants containing them.

Various additives are in general added to mineral and syntheticlubricants in order to improve the performance characteristics of theselubricants. There is in particular a need for additives able to protectthe devices to be lubricated from frictional wear. The requirement whichwear inhibitors of this kind have to meet is that they increase theload-bearing capacity of the lubricants and do not have a corrosiveaction on the metal parts to be protected. Phenol-containingdithiophosphates as lubricant additives have been described in the U.S.Pat. No. 3,017,422, in the G.B. Pat. No. 1,506,917 and in the U.S. Pat.No. 3,745,148. These however do not satisfy, or only partially satisfy,the strict requirements which a high-pressure antiwear additive has tomeet.

There has now been found a class of phenol-containing dithiophosphatesin which the dithiophosphate part is linked in a quite specific mannerto the phenolic molecule. These compounds impart to lubricants, inaddition to having therein a good anti-oxidation and anti-corrosionaction, excellent extreme pressure and antiwear properties. Furthermore,the novel compounds are characterised by negligible formation ofsediment and by no formation of ash.

The novel compounds correspond to the general formula I ##STR3## whereinR₁ and R₂ independently of one another are each C₁ -C₁₂ -alkyl, or theyare phenyl, C₇ -C₉ -aralkyl or C₅ -C₇ -cycloalkyl each of which isunsubstituted or substituted by 1 to 3 alkyl groups having a total of 1to 12 C atoms, R₂ in addition being hydrogen or chlorine, R₃ is hydrogenor methyl, R₄, R₆ and R₈ independently of one another are each hydrogenor C₁ -C₂₀ -alkyl, with the proviso that R₄, R₆ and R₈ as alkyl groupscontain all together 1 to 20 C atoms, R₉ is hydrogen, methyl or halogen,and one of the radicals R₅ and R₇ is a group of the formula II ##STR4##and the other is hydrogen, wherein R₁₀ and R₁₁ independently of oneanother are each C₁ -C₃₀ -alkyl or C₂ -C₁₀ -alkoxyalkyl, or R₁₀ and R₁₁together are a group of the formula III

    --(R.sub.12)C(R.sub.13)-[(R.sub.14)C(R.sub.15)].sub.m --(R.sub.16)C(R.sub.17)--                                 (III)

wherein m is nought or 1, and R₁₂, R₁₃, R₁₄, R₁₅, R₁₆ and R₁₇independently of one another are each hydrogen or methyl.

R₁ and R₂ as C₁ -C₁₂ -alkyl are for example: methyl, ethyl, isopropyl,sec-butyl, tert-butyl, tert-amyl, n-hexyl, 1,1,3,3-tetramethylbutyl or1,1,3,3,5,5-hexamethylhexyl. Preferred alkyl groups have 1 to 8 C atoms.In preferred compounds, R₁ is also tert-butyl, tert-amyl or1,1,3,3-tetramethylbutyl.

When R₁ and R₂ are C₇ -C₉ -aralkyl, they can be benzyl, α-phenylethyl orα,α-dimethylbenzyl.

Where R₁ and R₂ are C₅ -C₇ -cycloalkyl, they can be cyclopentyl,cyclohexyl or cycloheptyl.

R₁ and R₂ as phenyl, aralkyl and cycloalkyl can be substituted with 1 to3 alkyl groups having all together 1 to 12 C atoms. Examples of alkylsubstituents of this kind are methyl, ethyl, isopropyl, n-butyl,sec-butyl, tert-butyl, n-hexyl, 1,1,3,3-tetramethylbutyl, n-nonyl,1,1,3,3,5,5-hexamethylhexyl or n-dodecyl.

The preferred meaning of R₃ is hydrogen.

R₄, R₆ and R₈ as C₁ -C₂₀ -alkyl are for example methyl, ethyl,isopropyl, sec-butyl, n-hexyl, 2,2,4,4-tetramethylpentyl, straight-chainor branched-chain dodecyl, tetradecyl, octadecyl or eicosyl. Preferredalkyl groups have 1 to 6 C atoms; particularly preferred are ethylgroups and especially methyl groups. R₉ as halogen is in particularchlorine.

The sum of the C atoms contained in the substituents has to be in all 1to 20, preferably 1 to 6, and in particular 1 and 2. Among the mostimportant compounds of the formula I are those wherein one of theradicals R₄, R₆ and R₈ is hydrogen, and the other two are methyl; alsothose in which two of the radicals R₄, R₆ and R₈ are hydrogen, and thethird is methyl; and finally those in which R₄, R₆ and R₈ are eachhydrogen.

When R₁₀ and R₁₁ are C₁ -C₃₀ -alkyl, they can be for example: methyl,ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-hexyl,n-octyl, 2-ethylhexyl, 6-methylheptyl, n-octyl or straight-chain orbranched-chain nonyl, decyl, dodecyl, tridecyl, tetradecyl, octadecyl,eicosyl, docosyl, tetracosyl or triacontyl. Long-chain alkyl groupsconsist in general of isomeric mixtures.

When R₁₀ and R₁₁ are C₂ -C₁₀ -alkoxyalkyl, the alkyl moiety can contain1 to 3 C atoms and the alkoxy moiety 1 to 8 C atoms, such as inmethoxymethyl, ethoxymethyl, 2-methoxyethyl, 2-ethoxyethyl,2-n-butoxyethyl, 3-n-butoxypropyl, 2-octoxyethyl or methoxypropyl.

When R₁₀ and R₁₁ together are an alkylene group of the formula V, it isfor example alkylene-1,2, such as 1-methylethylene-1,2,1,1-dimethylethylene-1,2, 1,1,2-trimethylethylene-1,2,1,1,2,2-tetramethylethylene-1,2, propylene-1,3, 1-methylpropylene-1,3,1,1,3-trimethylpropylene-1,3 or 2,2-dimethylpropylene-1,3.

Preferred compounds correspond to the formula I wherein R₁ and R₂independently of one another are C₁ -C₈ -alkyl, and R₂ is in additionhydrogen, R₃ is hydrogen or methyl, R₄, R₆ and R₈ independently of oneanother are each hydrogen or C₁ -C₆ -alkyl, with the proviso that R₄, R₆and R₈ as alkyl groups have all together 1 to 6 C atoms, R₉ is hydrogen,and one of the radicals R₅ and R₇ is a group of the formula II and theother is hydrogen, wherein R₁₀ and R₁₁ independently of one another areeach C₁ -C₂₂ -alkyl, or R₁₀ and R₁₁ together are a group of the formulaIII wherein m and R₁₂ to R₁₇ have the meanings defined above.

Particularly preferred compounds correspond to the formula I wherein R₁is tert-butyl, tert-amyl or 1,1,3,3-tetramethylbutyl, R₂ is C₁ -C₈-alkyl, R₃ is hydrogen, R₄, R₆ and R₈ independently of one another areeach hydrogen, methyl or ethyl, with the proviso that R₄, R₆ and R₈ asalkyl groups have 1 to 2 C atoms, R₉ is hydrogen, and one of theradicals R₅ and R₇ is a group of the formula II and the other ishydrogen, whereby R₁₀ and R₁₁ independently of one another are each C₁-C₂₂ -alkyl, or together are a group of the formula III, wherein m andR₁₂ to R₁₇ have the meanings defined above.

Typical representatives of the class of substances according to theinvention are for example: ##STR5##

In the formulae IV to VIII, one of the radicals R₅ and R₇ is hydrogen,and the other is a group of the formula II wherein R₁₀ and R₁₁ have thefollowing meanings:

    ______________________________________                                        No.            R.sub.10     R.sub.11                                          ______________________________________                                        IV-VIII 1.a/b  isopropyl    isopropyl                                         IV-VIII 2.a/b  2-ethylhexyl 2-ethylhexyl                                      IV-VIII 3.a/b  methyl       methyl                                            IV-VIII 4.a/b  octadecyl    n-butyl                                           IV-VIII 5.a/b  docosyl      docosyl                                           IV-VIII 6.a/b  tridecyl     tridecyl                                          ______________________________________                                        No.            R.sub.10 + R.sub.11                                            ______________________________________                                        IV-VIII 7.a/b  1,1,3-trimethylpropylene-1,3                                   IV-VIII 8.a/b  2,2-dimethylpropylene-1,3                                      IV-VIII 9.a/b  ethylene-1,2                                                   ______________________________________                                    

As compounds (a) are denoted those in which R₅ is hydrogen, and R₇ is agroup of the formula II in which R₁₀ and R₁₁ have the meanings given inthe Table. As compounds (b) are denoted those in which R₅ is a group ofthe formula II wherein R₁₀ and R₁₁ have the given meanings, and R₇ ishydrogen.

The compounds of the formula I are produced in a manner known per se,for example by the addition reaction of a compound of the formula IX##STR6## wherein R₁₀ and R₁₁ have the meanings defined above, with analkene of the formula X ##STR7## wherein the symbols R₁, R₂, R₃, R₄, R₆,R₈ and R₉ have the meanings defined above.

The addition reaction can be performed in an inert solvent or preferablywithout solvent at temperatures of 0°-180° C., particularly 50°-150° C.,and optionally in the presence of a radical initiator.

Suitable solvents are optionally chlorinated, aliphatic or aromatichydrocarbons, such as special grades of petroleum spirit, or hexane,heptane, methylene chloride, 1,2-dichloroethane, benzene, chlorobenzene,dichlorobenzene, toluene or xylene; or ethers, such as diethyl ether,dioxane or tetrahydrofuran.

Radical initiators usable for the radically catalysed addition reactionare for example in particular: peroxy and azo compounds, as well as UVlight. Customary peroxy compounds are hydrogen peroxide, di-t-butylperoxide, cumene hydroperoxide or dibenzoyl peroxide. A suitable azocompound is especially α,α'-azodiisobutyric acid nitrile.

There is obtained by the addition reaction described, besides thecompound of the formula I in which R₅ is hydrogen and R₇ is a group ofthe formula II, as a rule the isomeric compound of the formula I inwhich R₅ is a group of the formula II and R₇ is hydrogen. The separationof the isomers is performed in a known manner. Usually however theisomeric mixture is used directly for the application as lubricantadditives.

The compounds of the formula IX are known compounds and are readilyavailable commercially.

The compounds of the formula X are likewise known, or, in cases wherethey are new, they can be produced in a known manner. One method forproducing them is described for example in the U.S. Pat. No. 3,526,668.

Even in very small amounts, the compounds of the formula I are effectiveas high-pressure additives in lubricants. Thus, mineral and syntheticlubricating oils, and also mixtures thereof, which contain 0.001 to 5percent by weight, preferably 0.02 to 3 percent by weight, relative tothe lubricant, of a compound of the formula I display excellenthigh-pressure lubricating properties which are clearly manifested ingreatly reduced wear phenomena on the parts in contact which have beenlubricated. The lubricants which can be used are commonly known to thoseskilled in the art, and are described for example in "SchmiermittelTaschenbuch" ["Lubricants Handbook"](Huthig Verlag, Heidelberg, 1974).

The lubricating-oil formulation can additionally contain other additiveswhich are added in order to improve certain basic oil properties,additives such as antioxidants, metal passivators, rust inhibitors,agents for improving the viscosity index, pour-point depressors,dispersants/detergents and other additives which protect against wear.

Examples of antioxidants are:

(a) alkylated and non-alkylated aromatic amines and mixtures thereof,for example: dioctyldiphenylamine, mono-t-octylphenyl-α- and-β-naphthylamines, phenothiazine, dioctylphenothiazine,phenyl-α-naphthylamine and N,N'-di-sec-butyl-p-phenylenediamine;

(b) sterically hindered phenols, for example 2,6-di-tert-butyl-p-cresol,4,4'-bis-(2,6-diisopropylphenol), 2,4,6-triisopropylphenol,2,2'-thio-bis-(4-methyl-6-tert-butylphenol) and4,4'-methylene-bis-(2,6-di-tert-butylphenol);

(c) alkyl phosphites, aryl phosphites or aralkyl phosphites, forexample: trinonyl phosphite, triphenyl phosphite and diphenyldecylphosphite;

(d) esters of thiodipropionic acid or thiodiacetic acid, for example:dilauryl thiodipropionate or dioctyl thiodiacetate;

(e) salts of carbamic and dithiophosphoric acids, for example: antimonydiamyldithiocarbamate and zinc diamyldithiophosphate; and

(f) combinations of two or more antioxidants from the above, forexample: an alkylated amine and a sterically hindered phenol.

Examples of metal passivators are:

(a) for copper, for example: benzotriazole, tetrahydrobenzotriazole,2-mercaptobenzothiazole, 2,5-dimercaptothiadiazole,salicylidene-propylenediamine and salts of salicylaminoguanidine;

(b) for lead, for example: sebacic acid derivatives, quinizarine andpropyl gallate; and

(c) a combination of two or more of the above additives.

Examples of rust inhibitors are:

(a) organic acids and their esters, metal salts and anhydrides, forexample: N-oleoyl-sarcosine, sorbitane monooleate, lead naphthenate anddodecenylsuccinic anhydride;

(b) nitrogen-containing compounds, for example:

I. primary, secondary or tertiary aliphatic or cycloaliphatic amines andamine salts of organic and inorganic acids, for example oil-solublealkyl-ammonium carboxylates, and

II. heterocyclic compounds, for example: substituted imidazolines andoxazolines;

(c) phosphorus-containing compounds, for example: amine salts ofphosphoric acid partial esters;

(d) sulfur-containing compounds, for example: bariumdinonylnaphthalene-sulfonates and calcium petroleum sulfonates; and

(e) combinations of two or more of the above additives.

Examples of agents which improve the viscosity index are:polymethacrylates, vinylpyrrolidone/methacrylate copolymers,polybutenes, olefine copolymers and styrene/acrylate copolymers.

Examples of pour-point depressors are: polymethacrylates and alkylatednaphthalene derivatives.

Examples of dispersants/detergents are: polybutenylsuccinic acid imides,polybutenylphosphonic acid derivatives and hyperbasic sulfonates andphenolates of magnesium, calcium and barium.

Examples of other additives which provide protection against wear are:compounds which contain sulfur and/or phosphorus and/or halogen, such asvegetable oils treated with sulfur, zinc dialkyldithiophosphates,tritolyl phosphates, chlorinated paraffins, alkyl disulfides and aryldisulfides.

The Examples which follow further illustrate the invention.

EXAMPLE 1 ##STR8##

214 g of dithiophosphoric acid-O,O-diisopropyl ester are added undernitrogen to 246 g of 3-(3,5-di-t-butyl-4-hydroxyphenyl)-prop-1-ene, andwith the addition of 1 g of azodiisobutyric acid nitrile in severalportions the mixture is heated, with stirring, for 8-10 hours at90°-110° C. At the end of the reaction period, there is practically nofurther olefin detectable (thin-layer chromatography).

The substance is freed in vacuo (˜15 mm Hg/80° C.) from readily volatileimpurities. The isomeric mixture thus obtained forms a slightly brownishviscous oil, and can be used directly for application according to theinvention as a lubricant additive.

EXAMPLE 2 ##STR9##

By replacing the diisopropyl ester of Example 1 by the correspondingamount of dithiophosphoric acid-di-2-ethyl-n-hexyl ester, with otherwisethe same procedure, there is obtained the above isomeric mixture in theform of a viscous, almost colourless oil.

EXAMPLE 3 ##STR10##

With use of the corresponding cyclic O,O-diester of dithiophosphoricacid with 1,1,3-trimethyl-1,3-dihydroxypropane, there is obtained,analogously to Example 1, the above-given isomeric mixture in the formof a viscous, almost colourless oil.

EXAMPLE 4

The following values were determined using the Shell four-ball apparatus(Tentative method IP 239/69, extreme pressure and wear lubricant testfor oils and greases, four-ball machine).

                  TABLE                                                           ______________________________________                                        (1) I.S.L. = Initial Seizure Load: that is the load under                     which the oil film breaks down within a duration of load                      application of 10 seconds.                                                    (2) W.L. = Weld Load: that is the load under which the                        4 balls weld together within 10 seconds.                                      (3) W.S.D. = Wear Scar Diameter in mm: that is the mean                       wear diameter when a load of 40 kg is applied for 1 hour.                      Vitrea 41 (Shell trade name) was used as the base oil.                        Concentration of the stabiliser: 1 percent by weight.                        ______________________________________                                        Stabiliser                                                                            ISL (kg)    WL (kg)     WSD (mm)                                      ______________________________________                                        none    about 60    about 160   about 2.4                                     Example 1                                                                             100         240         0.4                                           Example 2                                                                             100         220         0.4                                           ______________________________________                                    

EXAMPLE 5 Oil-oxidation test, standard version according to ASTM D 2272(Rotary Bomb Oxidation Test)

An oil specimen of 50 ml of mineral oil, "Vitrea 41" (Shell trade name),with the addition of 0.25 g of stabiliser is oxidised, in a glassvessel, together with 5 ml of distilled water and a polished,catalytically acting copper coil, which has been washed with petroleumether, in an oxygen atmosphere. The glass vessel is in a stainless-steelbomb fitted with a pressure gauge. The bomb rotates axially at 100r.p.m., at an angle of 30° with the horizontal, in an oil bath at 150°C. Before heating commences, the oxygen pressure is initially about 6atm. (90 psi); it increases at 150° C. to nearly 14 atm. (200 psi) andthen remains constant until oxidation occurs. The test is terminatedwith a drop in pressure of 1.7 atm. (25 psi), and the time in minutesuntil that occurs is recorded.

    ______________________________________                                        Test results                                                                              Minutes until pressure drop                                       Stabiliser  of 25 psi occurs                                                  ______________________________________                                        none         16                                                               Example 1   193                                                               Example 2   120                                                               ______________________________________                                    

EXAMPLE 6 Oil-oxidation test according to IP 280, "CIGRE"

Modified version with soluble Cu and Fe catalyst.

Conditions: Introduction of oxygen for 4 hours at 150° C. (4 liters ofO₂ /h).

Determination of the acid number after end of test; table value: mg KOHconsumption per gram of test oil.

Stabiliser concentration: 0.5 percent by weight.

Test oil: mineral oil "Vitrea 41" (Shell trade name).

                  TABLE                                                           ______________________________________                                        Stabiliser    mg KOH/g                                                        ______________________________________                                        none          3.6                                                             Example 1     1.45                                                            Example 2     1.22                                                            ______________________________________                                    

What is claimed is:
 1. A compound of formula I ##STR11## wherein R₁ andR₂ independently of one another are each C₁ -C₈ -alkyl, and R₂ inaddition is hydrogen, R₃ is hydrogen or methyl, R₄, R₆ and R₈independently of one another are each hydrogen or C₁ -C₆ -alkyl, withthe proviso that R₄, R₆ and R₈ as alkyl groups have all together 1 to 6C atoms, R₉ is hydrogenand one of the radicals R₅ and R₇ is a group ofthe formula II ##STR12## and the other is hydrogen, wherein R₁₀ and R₁₁independently of one another are each C₁ -C₂₂ -alkyl, or R₁₀ and R₁₁together are a group of the formula III

    --(R.sub.12)C(R.sub.13)--[R.sub.14)C(R.sub.15)].sub.m --(R.sub.16)C(R.sub.17)--                                 (III)

wherein m is nought or 1, and R₁₂, R₁₃, R₁₄, R₁₅, R₁₆ and R₁₇independently of one another are each hydrogen or methyl.
 2. A lubricantcomposition comprising a mineral or synthetic lubricating oil or mixtureof said oils, and from 0.001 to 5% by weight, relevant to the oil, of acompound of formula I according to claim
 1. 3. A compound according toclaim 1 of the formula I wherein R₁ is tert-butyl, tert-amyl or1,1,3,3-tetramethylbutyl, R₂ is C₁ -C₈ -alkyl, R₃ is hydrogen, R₄, R₆and R₈ independently of one another are each hydrogen, methyl or ethyl,with the proviso that R₄, R₆ and R₈ as alkyl groups have 1 to 2 C atoms,R₉ is hydrogen, and one of the radicals R₅ and R₇ is a group of theformula II and the other is hydrogen, whereby R₁₀ and R₁₁ independentlyof one another are each C₁ -C₂₂ -alkyl, or together are a group of theformula III, wherein m and R₁₂ to R₁₇ have the meanings defined inclaim
 1. 4. A compound according to claim 1 of the formula I wherein twoof the radicals R₄, R₆ and R₈ are hydrogen, and the third is methyl. 5.A compound according to claim 1 of the formula I wherein one of theradicals R₄, R₆ and R₈ is hydrogen, and the other two are methyl.
 6. Acompound according to claim 4 of the formula I wherein R₄ is methyl, andR₆ and R₈ are hydrogen.
 7. A compound according to claim 4 of theformula I wherein R₆ is methyl, and R₄ and R₈ are hydrogen.
 8. Acompound according to claim 4 of the formula I wherein R₈ is methyl, andR₄ and R₆ are hydrogen.
 9. A compound according to claim 1 which is##STR13##